The present invention relates to light polarizers or more particularly to light polarizers having increased hydrolytic stability.
U.S. Pat. No. 4,025,688 teaches the manufacture of light polarizers by providing a film of polyvinyl alcohol with a dichroic stain such as iodine. The polarizer may optionally be supported by a layer of cellulose acetate butyrate bonded to the polarizer through a hydrophilic tie coat.
A problem with this type of polarizer is it demonstrates poor hydrolytic stability. That is, its polarizing efficiency, or ability to polarize light, decreases over time as heat and humidity increases. This tendency is disadvantageous for such uses as in liquid crystal displays especially automobile instruments which must function in a wide range of heat and humidity conditions.
Czechoslovakian Pat. No. 122,408 discloses a process for stabilizing polarizing film by exposure to radiation at a wavelength of less than 400 nm for three hours.
Russian Pat. No. 124,116 stretches a polyvinyl alcohol film heats it and then places the film into an iodized solution containing hydrobromic acid and hydriodic acid with subsequent washing and drying. There is no subsequent heating.